Valve spring compressors are well known and are essential devices for the removal of the relatively stiff rocker springs and the like in conventional automotive engines. Such a tool must be extremely sturdy to withstand repeated usage and yet be convenient for handling by the mechanic. Typically the tool is inserted in place over the valve spring and an initial adjustment performed in order to match the general spacing of the abutment means of the tool to the valve spring and associated components of the vehicle, and then the tool is actuated to compress the spring so that removal or replacement may be performed.
Another adjustment that is required of such tools is that the jaws be varied in spacing to accommodate different valve spring sizes or in fact be readily replaceable to accommodate different size ranges. Such separable jaw and frame structures are well established in the art being shown for example in U.S. Pat. Nos. Re. 19,414, 3,038,247, 3,039,180 and 3,668,765. In these prior art devices the valve engaging jaws are typically secured to the frame by means of threaded fasteners and in order to replace the set of jaws on the tool it is necessary to fully withdraw the fasteners so that a new set of jaws may be positioned thereon. It is also typical of such prior art devices that the adjustment member for setting the spacing of the individual jaw segments need be removed as well as typically it is positioned intermediate the other fastening devices. Such interchange therefore typically required the removal of four or five screws or bolts, thereby freeing the jaws completely and requiring that the new set of jaws be held temporarily in place by hand while the fasteners were rethreaded into position, this being a relatively inconvenient procedure requiring the starting of each of the threaded members and the prealignment of the component members of the jaw set.
Further, in such arrangement it was common that one or more of the threaded members might be lost and that the tool might be used in such incomplete state, and which under the relatively high spring forces encountered, resulted in a relatively unsafe structure.